The present invention relates to a belt conveyor. More particularly, it relates to a belt conveyor which has a trough-shaped upper load-carrying run whose inclined lateral portions are supported by inclined supporting rollers, whereas a flat central portion of the run is in frictional contact with one run of a friction belt guided by bearing rollers.
Belt conveyors of the above-mentioned general type are disclosed in the German Pat. No. 592,657 and German Offenlegungsschrift No. 2,412,156. It has been recognized that in such belt conveyors the load which is required for transmission of the driving force and applied by the carrying belt to the friction belt, is distributed nonuniformly over the contacting surfaces of the belts. Since both the carrying belt and the friction belt are flexible in a certain range, considerable tension develops because of the varying forces between the lower surface of the carrying belt and the upper surface of the friction belt. This results in the driving force being transmitted to the carrying belt only under conditions of relatively great friction slip, which leads to a considerable wear between the carrying belt and the friction belt, so that finally the carrying belt does not run parallel to the friction belt. Especially in high-speed conveyors the latter-mentioned disadvantage has the result that the carrying belt, in spite of the fact that it is supported by the lateral supporting rollers, becomes separated from the friction belt and loses its frictional contact with the same.
In order to eliminate the above-mentioned disadvantages, a belt conveyor with an intermediate drive has been proposed in the German Pat. No. 907,877. This intermediate drive is formed as a sprocket chain on which a plurality of discs are consecutively arranged. The discs have a friction face which engages with the central region of the conveyor belt and drives both runs of the conveyor belt by the friction contact. The discs of the sprocket chain, provided with friction layers form an interrupted support so that the band tension between the conveyor belt and the discs can be compensated.
The above-described known conveyor belt with the intermediate drive has the disadvantage that the sprocket chain with the bearing discs can provide for only a small speed of movement. A further disadvantage of this conveyor belt with the intermediate drive is that the conveyor belt sags between the bearing discs and thereby rubs on the edges of the bearing discs, which results in a high degree of wear.